1. Technical Field
The present invention relates to a technique of reducing display defects in a liquid crystal panel.
2. Related Art
A liquid crystal panel is configured such that a liquid crystal is interposed between a pair of substrates held with a predetermined gap therebetween. Specifically, the liquid crystal panel has a configuration in which pixel electrodes are arranged in a matrix form for each pixel on one substrate, a common electrode is provided on the other substrate so as to be shared by the respective pixels, and the liquid crystal is interposed between the pixel electrodes and the common electrode. When a voltage corresponding to a gradation level is applied and held between the pixel electrode and the common electrode, the alignment state of the liquid crystal is defined for each pixel, whereby transmittance or reflectance is controlled. Therefore, in the configuration above, it can be said that among the electric field acting on the liquid crystal molecules, only a component in the direction (or the opposite direction) from the pixel electrode towards the common electrode, namely in the direction perpendicular (vertical) to the substrate surface contributes to display control.
However, as the pixel pitch has narrowed with further miniaturization and higher definition in recent years, the effect of an electric field which is generated between the adjacent pixel electrodes, namely an electric field in the direction parallel (horizontal) to the substrate surface has become unignorable. For example, when a horizontal electric field is applied to a liquid crystal that is designed to be driven by a vertical electric field such as in a VA (Vertical Alignment) or TN (Twisted Nematic)-mode liquid crystal, there is a problem in that alignment defects (namely, reverse tilt domain) occur in the liquid crystal, thus causing display defects.
Various proposals have been made in order to reduce the effect of reverse tilt domain. For example, JP-6-34965 (FIG. 1) discloses a new liquid crystal panel structure in which the shape of a light shielding layer (opening) is defined in conformity with the pixel electrode. Moreover, JP-2009-69608 (FIG. 2) discloses a technique in which when determining that reverse tilt domain occurs when an average luminance value calculated from a video signal is equal to or lower than a threshold value, video signals having a luminance value equal to or higher than a preset value are clipped away.
However, the technique of reducing the reverse tilt domain by devising a new liquid crystal panel structure has a drawback in that the aperture ratio is likely to decrease and it is difficult to apply the technique to a liquid crystal panel which is not manufactured in advance so as to have the new structure. On the other hand, the technique of clipping away the video signals having a luminance value equal to or higher than a preset value has a drawback in that the brightness of displayed images is limited to the preset value.